It's cute console girls doing cute console things
If you want a quick opinion on the series
Hyper Dimension Neptunia - Watch the cutscenes, the games combat is complete trash, %chance for using a health pot to FAIL?

Hyper Dimension Neptunia mk2 - Play the game, the story is pretty cool, the characters are cool and it's a jolly old time. Play this before Victory

Hyper Dimension Neptunia Victory - Play this after mk.2, the everything is improved, esp the framerates (lord knows sub 20 frames isn't fun). Be ready to switch it to Japanese dubbing because the english dub is extremely lazily done compared to Mk.2. Less than half the games lines are dubbed into english.

It's also very anime and very niche, don't play it if you are some nerd who hates anime or cute anime shit.